JP6727322B2 - Hydrophobic polyethylene membrane for use in degassing, degassing and membrane distillation processes - Google Patents

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is the benefit of US Provisional Application No. 62/310378, filed Mar. 18, 2016, the entire contents of which are hereby incorporated by reference. Insist.

Hydrophobic membranes are used in various processes including degassing, degassing and membrane distillation.

Degassing operations are performed in various manufacturing processes, including pharmaceutical manufacturing, to maintain a sterile environment within the bioreactor. Typically, the degassing operation allows gas to escape from a chamber, such as a reaction chamber, while preventing water and pathogens such as bacteria, viruses and fungi from entering the chamber. In this sense, the membrane behaves like a filter. Degassing devices are known in the art, such as those described in US Pat. Nos. 8,852,324 and 8,430,114, and hydrophobic membranes are typically part of them and similar devices.

For each of the above three processes, the membrane should meet certain performance requirements. The membrane should be as hydrophobic as possible, which prevents water from passing through the membrane. Relatedly, the membrane should not wet when contacted with water or another wetting solvent such as 40% isopropyl alcohol (IPA) in water. The pore size of the membrane should be small enough to prevent pathogens from crossing the membrane. The membrane must be sterilizable, which means that the membrane should maintain its structural integrity upon exposure to gamma radiation. Further, a membrane that allows a high flow rate of gas is desirable.

Although membranes are currently used in degassing operations, it is desirable to improve their performance with respect to one or more of the criteria outlined above. For example, polytetrafluoroethylene (PTFE) membranes are hydrophobic, allowing high air permeability, but cannot be gamma sterilized. Polyvinylidene fluoride (PVDF) membranes do not have high air permeability and are not as hydrophobic as PTFE, so they wet under certain conditions. Polyethylene membranes, including ultra high molecular weight polyethylene membranes, are not as hydrophobic as PTFE and therefore are not considered readily suitable for use in wetting, degassing, degassing and membrane distillation. Therefore, a film having improved properties with respect to one or more of the above criteria is desirable.

Embodiments of the present disclosure have an air permeability in the range of about 4.9 slpm/cm ^{2 to} about 9.4 slpm/cm ² , when measured at about 10 psi, in the range of about 15 dyne/cm to about 25 dyne/cm. Surface energy, liquid entry pressures in the range of about 5 psi to about 25 psi, and perfluorinated monomers that change the surface energy of one or more surfaces of the membrane, as measured in a 80:20 methanol:water solution. Including a surface modified porous polyethylene membrane having. The molecular weight of the polyethylene membrane can range from about 2,000,000 daltons to about 9,000,000 daltons in some embodiments. The perfluorinated monomer can be a perfluoroacrylate or a perfluoro-n-alkyl acrylate such as perfluoro-n-octyl acrylate. In some versions, the air permeability, when measured at about 10 psi, about 4.9slpm / cm ² - when in the range of about 6.1slpm / cm ^2, or measured at about 10 psi, about 5 It can be 0.4 slpm/cm ² . In some versions, the surface energy can be in the range of about 21 dyne/cm to about 23 dyne/cm, or about 21.5 dyne/cm. In some versions, the liquid entry pressure is in the range of about 20 psi to about 25 psi when measured in a methanol:water 80:20 solution, or when measured in a methanol:water 80:20 solution. It can be about 22 psi. In one particular version, the air permeability is about 5.4 slpm/cm ² , the surface energy is about 21.5 dyne/cm, and the liquid entry pressure is methanol:water 80 when measured at about 10 psi. : 22 psi when measured in a 20 solution. In some versions of the disclosure, the membrane may be uniaxially or biaxially stretched prior to modifying the surface of the membrane. The membrane is bacteria-retentive as determined by ASTM F838-05 (2013).

One embodiment of the present disclosure is a vent membrane comprising an expanded porous polyethylene membrane and a perfluorinated monomer that modifies one or more surfaces of the expanded porous polyethylene membrane; the vent membrane is ASTM F838-05/R( 2013) and the air permeability in the range of about 4.9 slpm/cm ^{2 to} about 9.4 slpm/cm ² when measured at about 10 psi; and about 15 dyne/cm −. It has a surface energy in the range of about 25 dyne/cm.

In some versions, the molecular weight of the polyethylene membrane is about 1,000,000 Daltons-about 9,000,000 Daltons or about 1,500,000 Daltons-about 2,500,000 Daltons.

In some embodiments of the vent membrane, the polyethylene membrane is biaxially stretched either before or after modifying the surface of the membrane. In some disclosed embodiments, the vent membrane has a tensile stress measured in the longitudinal direction of about 8 MPa to about 12 MPa in megapascals and about 0.2 mm/mm to about 0.3 mm/mm/mm. and a vent membrane having a tensile strain of from about 5 MPa to about 8 MPa in megapascals measured in the cross-web direction and a millimeter/millimeter after gamma ray treatment of the vent membrane with a gamma ray dose of at least about 25 kGy. It has a tensile strain of about 0.3 mm/mm to about 0.5 mm/mm.

In some embodiments of the present disclosure, the expanded porous polyethylene membrane is ultra high molecular weight polyethylene. In another embodiment, the stretched polyethylene membrane is polyethylene having a molecular weight that can be in the range of about 100,000 daltons to about 1,000,000 daltons. The molecular weight of polyethylene can be determined using the Mark-Houwink equation described herein.

In some embodiments of the vent membrane, the perfluorinated monomer is a perfluoro-n-alkyl acrylate, such as perfluoro-n-octyl acrylate.

In some embodiments of the vent membrane, the vent membrane has a surface energy within the range of about 21 dyne/cm to about 23 dyne/cm.

In some embodiments of the vent membrane, the vent membrane prior to gamma-ray treatment with a gamma-ray dose has a tensile stress measured in the longitudinal direction of about 12 MPa to about 16 MPa in megapascals and about 0.5 mm in millimeters/millimeters. /Mm-having a tensile strain of about 0.9 mm/mm, and the vent membrane has a tensile stress of about 6 MPa to about 8.5 MPa in megapascals measured in the cross-web direction and 1. It has a tensile strain of 0 mm/mm-1.8 mm/mm.

Another embodiment of the present disclosure is a vent membrane that includes a gamma radiation stable porous polymer membrane and a perfluorinated monomer that modifies one or more surfaces of the porous polymer membrane. The vent membrane is bacteria-retentive as determined by ASTM F838-05. Vent membranes when measured at about 10 psi, about 4.9slpm / cm ² - an air permeability in the range of about 9.4slpm / cm ^2, and about 15 dyne / cm- range of about 25 dyne / cm Has a surface energy within. After gamma irradiation of the vent membrane with a gamma dose of at least about 25 kGy, the vent membrane has a tensile strain measured in the longitudinal direction of about 0.2 mm/mm to about 0.3 mm/mm, and The vent membrane has a tensile stress measured in the crossweb direction of about 5 MPa to about 8 MPa in megapascals and a tensile strain of about 0.3 mm/mm to about 0.5 mm/mm in millimeters/millimeters.

In another aspect, described herein is a method of making a grafted porous polyethylene (PE) membrane, which in some versions can be an ultra high molecular weight polyethylene membrane (UPE). The method comprises the steps of contacting a polyethylene membrane with an alcohol solution containing benzophenone, contacting the polyethylene membrane with a grafting solution, and exposing the membrane to electromagnetic radiation, thereby producing a grafted porous polyethylene membrane. Can be included. The molecular weight of the polyethylene membrane can be in the range of about 1,000,000 Daltons-about 9,000,000 Daltons or about 1,500,000 Daltons-about 2,500,000 Daltons. Grafting solution may comprise a perfluorinated monomer and decamethyl tetrasiloxane. In some cases, the perfluorinated monomer is perfluoroacrylate, or a perfluoro-n-alkyl acrylate such as perfluoro-n-octyl acrylate. Grafted porous membrane, about when measured at 10 psi (69 kPa), about 4.9slpm / cm ² - such as in the range from about 6.1slpm / cm ² or about 5.4 SLPM / cm ^2, about 4.9Slpm /Cm ² -which may have an air permeability in the range of about 9.4 slpm/cm ² . The grafted porous membrane can have a surface energy in the range of about 21 dyne/cm to about 23 dyne/cm or in the range of about 15 dyne/cm to about 25 dyne/cm, such as about 21.5 dyne/cm. The grafted porous membrane should have a liquid entry pressure in the range of about 5 psi to about 25 psi, such as in the range of about 20 psi to about 25 psi, or about 22 psi, all measured in a methanol:water 80:20 solution. You can

The membranes described herein provide improved flow properties for use in degassing, degassing and membrane distillation processes. Significant stretching of a PE or UPE membrane increases the air permeability, as measured by air permeability, but does not correspondingly increase the pore size. Modification of the membrane surface with a hydrophobic monomer results in a more hydrophobic membrane. The membrane also maintains its structural integrity, which is important when pressure is applied to the membrane. Further, the resulting grafted PE or UPE membrane can be sterilized by exposure to gamma rays.

The foregoing will become apparent from the following more detailed description of example embodiments of the invention, in which like reference characters are used in the accompanying drawings to refer to the same parts throughout the various drawings. The drawings are not necessarily to scale and focus on the description of embodiments of the invention.

3 is a scanning electron microscopy (SEM) image of a symmetrical unstretched UPE film. 3 is a scanning electron microscopy (SEM) image of a symmetrical stretched UPE film. A 5000x magnification was used in both Figures 1A-B. FIG. 3 is a diagram showing stress-strain curves in a non-stretched UHMWPE film (blue) and a stretched UHMWPE film (red) in a machine direction (MD) (FIG. 2A) direction and a cross web (CW) (FIG. 2B) direction. After stretching, the tensile fracture strain of the film is reduced to about 1/8 in MD and 5.5 in CW. Longitudinal (MD) (FIG. 3A) direction and cross-web (CW) (FIG. 3B) in stretched UHMWPE membrane (green dotted line), gamma exposed stretched UHMWPE membrane (red) and gamma exposed stretched and surface modified UHMWPE membrane (blue). It is a figure which shows the stress-strain curve of () direction. The tensile fracture strain of the stretched film and the surface modified-stretched film was reduced by approximately 2.5 times in MD and 3.3 times in CW after the gamma ray exposure and before the gamma ray exposure. The tensile fracture strains of modified and unmodified stretched membranes are similar after gamma-ray exposure, indicating a minimal effect of surface modification on the mechanical properties of stretched membranes. It is an example of an IR spectrum using the extension film of Example 5 before (dotted line) and after grafting (solid line). The spectra after grafting were shifted higher by 0.6 absorbance units for easier viewing. After surface modification, graft film is, 1760 cm ^-1 (corresponding to the ester group) and the range of 1289-1114cm ^-1 - shows characteristic peaks at (carbon corresponding to fluorine stretch).

The present invention is illustrated and described with reference to particular example embodiments thereof, in which various forms and details are set forth without departing from the scope of the invention, which is encompassed by the appended claims. Those of ordinary skill in the art will appreciate that changes may be made.

While various compositions and methods are described, it should be understood that the invention is not limited thereto, as the particular compositions, designs, techniques or protocols described may vary. Also, the terminology used in the description is for describing only the particular version(s) and is not intended to limit the scope of the invention, which is limited only by the scope of the appended claims. Should be understood.

As used in this specification and the appended claims, the singular forms “a”, “an” and “the” also include plural referents unless the context clearly dictates otherwise. It must be noted. Thus, for example, a reference to a "membrane" is a reference to one or more membranes and equivalents thereof known to those of skill in the art. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Methods and materials similar or equivalent to those described herein can be used in the practice or testing of versions of the present invention. All publications mentioned herein are incorporated by reference in their entirety. Nothing herein is to be construed as an admission that the invention is not entitled to antedate such disclosure by virtue of prior invention. "Optionally" or "optionally" may or may not cause the subsequently described event or situation, and the explanation is that the event is It is meant to include cases where they occur and cases where no event occurs. All numbers herein may be modified by the term "about," whether or not explicitly stated. The term "about" generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (ie, having the same function or result). In some versions, the term "about" refers to ±10% of the stated value, and in other versions, the term "about" refers to ±2% of the stated value. Although the compositions and methods are described by the expression "comprising" (which is taken to mean "including but not limited to") various ingredients or steps, the compositions and methods are , Can also be “consistently of” or “consisting of” various components and steps, such terminology being used to refer to a group of substantially closed elements or closed elements. It should be construed as defining a group.

A description of example embodiments of the invention follows.

Vent membranes in embodiments of the present disclosure include gamma radiation stable porous polymeric membranes that include perfluorinated monomers that modify one or more surfaces of the porous membrane. These vent membranes are hydrophobic and bacteria-retentive. In some embodiments of the present disclosure, the vent membrane comprises an expanded porous polyethylene membrane that includes a perfluorinated monomer that modifies one or more surfaces of the polyethylene membrane. These vent membranes are hydrophobic, gamma sterilizable, bacteria-retaining, and have a higher air permeability than non-stretched polyethylene membranes.

To produce membranes with improved performance properties and hydrophobicity, gamma-stable porous polymer membranes such as UPE membranes are modified in two ways. First, the membrane is stretchable, which improves the air permeation properties without significantly increasing the pore size of the membrane. In particular, stretched UPE membranes have the indicated degree of increase in air permeability compared to non-stretched UPE membranes, as measured by the air permeability test described in the General Experimental Part. Notably, this significant increase in air permeability was not accompanied by a similar drop in visual bubble point, a test to assess membrane pore size, also described in the General Experimental Section. In one example embodiment, the air permeability is improved from about 0.49 standard liters/minute/cm ² (membrane area) of the unstretched UPE membrane to about 5.9 standard liters/minute/cm ² of the stretched UPE membrane. did. In the same example embodiment, the visual bubble point of the stretched UPE membrane measured in an IPA:water 60:40 solution dropped from about 32 psi (221 kPa) to about 19 psi (131 kPa). In another example embodiment, stretching increased the air permeability from about 1.97 slpm/cm ² to about 9.4 slpm/cm ² , but the visual bubble measured in IPA:water 60:40 solution. The point only dropped from about 19 psi to about 12 psi.

Second, the surface of the membrane can be modified with monomers to lower the surface energy of the membrane, which corresponds to an increase in hydrophobicity. In one particular example embodiment, the grafted UPE membrane has a lower surface energy than PTFE, which is a highly hydrophobic membrane.

Typically, the membrane is stretched first and then the monomer is grafted onto the surface of the membrane. However, it is also possible to first graft the monomer onto the membrane and then stretch the membrane.

The surface modified polyethylene porous membranes described herein have properties that make them particularly useful for degassing, degassing and membrane distillation processes. In particular, the membrane achieves a high air permeability, thus facilitating the flow of air or other gas through the membrane. The membrane also has a low surface energy such that it is hydrophobic, typically equal to or more hydrophobic than the PTFE membrane. In addition, the membrane has a liquid entry pressure equal to or higher than the 0.2 micron PTFE membrane liquid entry pressure.

In some versions, the vent membrane has an air permeability in the range of about 4.9 slpm/cm ^{2 to} about 9.4 slpm/cm ² when measured at about 10 psi (69 kPa). In another embodiment, the membrane has an air permeability in the range of about 4.9 slpm/cm ^{2 to} about 6.1 slpm/cm ² when measured at about 10 psi (69 kPa). In another version, the membrane has an air permeability of about 5.4 slpm/cm ² when measured at about 10 psi (69 kPa). Air permeability can be evaluated according to the air permeability test described in the General Experimental Section.

In some versions, the membrane has a surface energy in the range of about 15 to about 25 dyne/cm. In other versions, the membrane has a surface energy in the range of about 21 to about 23 dyne/cm. In yet another version, the membrane has a surface energy in the range of about 21.5 dyne/cm. Surface tension or surface energy can be evaluated according to the test described in Example 6.

In some versions, the membrane has a liquid entry pressure in the range of about 15 to about 25 psi measured in a methanol:water 80:20 solution. In other versions, the membrane has a liquid entry pressure in the range of about 20 to about 25 psi when measured in a methanol:water 80:20 solution. In yet another version, the membrane has a liquid entry pressure of about 22 psi when measured in a methanol:water 80:20 solution. The liquid entry pressure can be evaluated according to the liquid entry pressure test described in Example 7 _[A1] .

A polyethylene porous membrane that can be stretched and grafted is such that a gamma dose of about 25 kGy changes the tensile strength of the stretched porous polyethylene membrane by less than about 60% in the machine direction and less than about 70% in the crossweb direction. However, those that are stable against gamma rays can be included. In some embodiments, the polyethylene including the porous membrane can have a molecular weight of greater than about 1,000,000 daltons and less than about 6,000,000 daltons.

Expanded porous polyethylene membranes can be identified by the high orientation of the polymer chains compared to more amorphous non-expanded porous polyethylene membranes. High orientation or crystallinity of polymer chains can be measured by X-ray diffraction of stretched porous membranes compared to non-stretched membranes or by differential scanning calorimetry (DSC). The high orientation or crystallinity of the polymer chains in the stretched film can also be measured by the tensile strength of the material.

In embodiments of the present disclosure, the tensile strain at break of the membrane is reduced by approximately one-eighth MD and about one-fifth CW after stretching. In some embodiments, the non-expanded porous polyethylene membrane has a tensile stress measured in the longitudinal direction of about 10 MPa to about 14 MPa in megapascals and about 4.5 mm/mm to about 5.5 mm in millimeters/millimeters. A non-stretched membrane having a tensile strain of /mm and a tensile stress of about 6.5 MPa to about 8.5 MPa in megapascals measured in the cross-web direction and about 7.0 mm/mm in millimeters/mm. -Has a tensile strain of about 9.5 mm/mm. In some embodiments, the expanded porous polyethylene membrane has a tensile stress measured in the longitudinal direction of about 12 MPa to about 16 MPa in megapascals and about 0.5 mm/mm to about 0.9 mm/mm/mm. and a vent membrane having a tensile strain of about 6 MPa to about 8.5 MPa in megapascals measured in the cross-web direction and about 1.0 mm/mm to about 1. It has a tensile strain of 8 mm/mm.

The gamma treatment of the porous membranes, vent membranes and vent filters disclosed herein can be at a dose of about 25 kGy or above about 25 kGy. In some embodiments, the vent membrane has a tensile stress measured in the longitudinal direction of about 8 MPa to about 12 MPa in megapascals and a tensile stress of about 0.2 mm/mm to about 0.3 mm/mm in millimeters/millimeters. The vent membrane can be strained, and the vent membrane can have a tensile stress of about 5 MPa to about 8 MPa in megapascals measured in the cross-web direction and a millimeter/millimeter after gamma ray treatment of the vent membrane with a gamma ray dose of at least about 25 kGy. It has a tensile strain of about 0.3 mm/mm to about 0.5 mm/mm. The high tensile stress and strain of the vent membrane, especially after gamma-ray treatment, is advantageous and can lead to bent membrane failure, sample contamination and process upset that can lead to bend of the vent membrane during use. Realize an integrated vent membrane.

The pore size of vent membranes and vent filters in embodiments of the present invention can be characterized by the bacterial retention or bubble point of the membrane. The vent membrane in the embodiments disclosed herein has a bacterial retention rate as a measure of the filter's ability to sterilize fluids, and (incorporated herein by reference in its entirety and also in the examples Pass the test described in ASTM F838-05 (2013). For example, in the Standard Test Method for Determining Bacterial Retention of Membrane Filters Utilized for Liquid Filtration, the filter can retain a minimum of 1×10 ⁷ colony forming units (cfu) of challenge bacteria (usually B. diminuta) per cm ² . Vent membranes in embodiments of the present disclosure, in addition to bacterial retention, include 60% IPA in 40% deionized water (v) less than about 12 pounds per square inch (psi) to about 32 pounds per square inch (psi). /V) may also be included. In some embodiments, the vent membrane bubble point is between about 12 psi and about 19 pounds per square inch.

In some embodiments, the base unmodified porous membrane is an ultra high molecular weight polyethylene membrane (also referred to as UHMWPE membrane or UPE membrane). Polyethylene membranes, especially UPE, are advantageous because the air permeability of UPE membranes can be significantly improved by biaxially stretching the membranes, compared to their unstretched counterparts. This is because the modulus increases by an order of magnitude or about 4 to about 12 times while not significantly weakening the membrane as measured by the tensile stress and strain of the membrane. Although the air permeability varies significantly, the membrane advantageously retains its relatively small pore size as compared to its non-stretched counterpart. The retention of small pores prevents bacteria from crossing the membrane during use.

In the claims and herein, references to "polyethylene membranes" and "PE" in embodiments of the present disclosure have a molecular weight of between about 100,000 daltons and about 9,000,000 daltons. Reference to porous polyethylene membranes having IPA bubble points between 10 psi and about 40 psi. References to "ultra high molecular weight polyethylene membranes" or "UPE membranes" in embodiments of the present disclosure have a molecular weight of between about 1,000,000 daltons and about 9,000,000 daltons, between about 10 psi and about 40 psi. Is a reference to a porous ultra high molecular weight polyethylene membrane having an IPA bubble point. Porous polyethylene membranes having an IPA bubble point between about 10 psi and about 40 psi, having a molecular weight less than the molecular weight of UPE are, for example, less than about 1,000,000 daltons or about 100,000 daltons-about 400,000 daltons. Is described by its molecular weight or molecular weight range. The molecular weight of various polyethylenes, including UPE, was determined by viscometrics according to test method ASTM D4020-05, the intrinsic viscosity [IV], and this value was calculated using the Mark-Houwink formula M=K[IV] ^α (wherein ASTM For D4020-5, the constant K is 53,700, α is 1.37, M has units of grams/molecule, and IV has units of deciliters/gram.). (See also, for example, HL Wagner, J. Phys. Chem. Ref. Data Vol. 14, No. 2, 1985). For UPEs having an intrinsic viscosity of between about 16 deciliters/gram (dL/g) and about 20 dL/g, the molecular weight range is about 2.4 million using the ASTM D4020-5 method and the Mark-Houwink equation. -Approximately 3.3 million.

UPE membranes are typically made from resins having a molecular weight higher than about 1,000,000. In some embodiments, the molecular weight of UPE is in the range of about 2,000,000 Daltons to about 9,000,000 Daltons. Although the examples and embodiments are described herein with reference to UPE, the principles are equally applicable to polyethylene membranes below the UPE cutoff value of about 1,000,000 Daltons.

To produce a polyethylene membrane, a polymer such as UPE is first extruded to form a porous membrane. In one embodiment, UPE having a molecular weight of about 2-4 million is combined with a solvent such as mineral oil and dioctyl phthalate to produce a slurry of about 10-20% solids composition. In another embodiment, UPE may be combined with a solvent such as mineral oil and dibutyl sebacate in a solid composition as low as 12% solids or as high as 19% solids. The slurry is placed in an extruder, such as a single or twin screw extruder, and the UPE is processed into a viscous mass (eg, gel or emulsion) at any temperature between 190°C and 275°C. The viscous mass is then passed through a die, resulting in a thick tape or film. The film is then quenched on a temperature controlled rotating drum having a temperature between 80°C and 110°C. The process of quenching the film turns the film from a gel-like viscous mass into a solid that can be handled as a web. The rotation speed of the drum can be changed so that the linear speed of the outer circumference is between 5 and 25 fpm. At this stage of the process, the membrane structure is at least partially formed, but the solvent may remain in the pore structure and in the polymer matrix, allowing greater migration of the polymer chains. After the quench drum, the membrane can be stretched in the machine direction between 0-200% with a vacuum roller, rubber roller or nip roller downstream. The final thickness of the film in this step may be 20 μm-100 μm.

After the film is formed, the solvent is removed by evaporation or extraction to obtain the base film. In some versions, the pore forming agent remains in the UPE until another stretching process is complete.

The UPE membranes described herein can have various geometric configurations such as flat plates, corrugated plates, pleated plates and hollow fibers, among others. The membrane can be, among other things, with or without web, net and cage support. The membrane support can be isotropic or anisotropic, skinned or unskinned, symmetrical or asymmetrical, any combination thereof, or one or more retaining layers and one or more supporting layers. Can be a composite membrane. The vent membrane in various embodiments can be bonded or secured to a gamma stable housing or other support by fusion bonding, bonding with a chemically compatible adhesive, or a machine such as an O-ring or gasket. It can be attached using a static seal. The housing can have a fluid inlet and a fluid outlet, and a vent membrane coupled to the housing fluidically separates the housing inlet and outlet. The vent membrane coupled to the housing is integral. In some embodiments, the vent membrane coupled to the housing or support is monolithic (no pinhole) and has one or more or all of the following: in megapascals measured longitudinally. Tensile stresses of about 8 MPa to about 12 MPa and tensile strains of about 0.2 mm/mm to about 0.3 mm/mm in millimeters/millimeters, and vent membranes after gamma ray treatment of the vent membrane with a gamma ray dose of at least about 25 kGy. It has a tensile stress of about 5 MPa to about 8 MPa in megapascals measured in the cross-web direction and a tensile strain of about 0.3 mm/mm to about 0.5 mm/mm in millimeters/millimeters, measured at about 10 psi. when in about 4.9slpm / cm ² - to be able to have an air permeability in the range of about 9.4slpm / cm ^2, it has a surface energy in the range of about 15 dyne / cm- about 25 dyne / cm , Having a liquid entry pressure in the range of about 5 psi to about 25 psi when measured in a methanol:water 80:20 solution, and is bacterial retentive as determined by ASTM F838-05/R (2013).

In one example of an asymmetric membrane, the pore size on one side and region of the membrane is larger than on the opposite side and region. In another example, an asymmetric structure can be present where the pore size on the opposite face (and region) of the membrane is larger and the central region of the membrane has a pore size smaller than either of the faces (eg, , Hourglass shape). In other versions, the membrane can have a pore structure that is substantially symmetrical over its thickness (substantially the same pore size over the thickness of the membrane).

In one aspect, the membrane can be further stretched after extraction to improve the air permeability of polyethylene membranes such as UPE membranes. In some embodiments, the membrane can stretch in the machine direction (longitudinal direction), the transverse direction (across the width of the membrane), or both. Unidirectional stretching is often referred to as uniaxial stretching, and bidirectional stretching is commonly referred to as biaxial stretching. Usually, but not always, the machine direction and the machine direction are perpendicular to each other.

During the stretching process, the polyethylene or UPE membrane is typically heated, which improves the stretching process. The temperature at which the membrane is heated can differ in stretching along the machine and cross directions. Typically, PE or UPE membranes are heated to between about 80° C. and about 120° C., for example about 100° C., with both longitudinal and transverse stretching.

After preheating as described in the preceding paragraph, the membrane can be stretched between two series of nip rollers (also called closed rollers). The speed of the second nip roller is typically greater than the speed of the first nip roller, which facilitates film stretching. Stretching with a nip roller stretches the membrane longitudinally, which increases the length of the membrane and reduces the width of the membrane. In some embodiments, the membrane is stretched longitudinally by a factor of about 2 to about 8 times. In another embodiment, the membrane is stretched longitudinally by a factor of about 2 to about 5 times. In yet another embodiment, the membrane is stretched longitudinally by a factor of about 2 to about 2.5. In some embodiments, the membrane is longitudinally stretched by a factor of about 1.7 to about 8. In another embodiment, the membrane is longitudinally stretched by a factor of about 1.7 to about 5. In yet another embodiment, the membrane is longitudinally stretched by a factor of about 1.7 to about 2.5.

The membrane is then stretched in the transverse direction (also referred to as the crossweb direction) by feeding the membrane into the tenter with a longitudinally advancing clip. The clip travels in a preheated oven and then in a V zone in the extension zone oven, which widens the width of the membrane. As an example, the preheat oven is at about 100°C and the stretching zone is at about 105°C. The membrane then proceeds in the annealing zone where the clips remain parallel. The temperature of the annealing zone is generally about 5 to about 15 degrees Celsius above the extension zone, but at least about 5 degrees Celsius below the melting point of the polymer. In some embodiments, the membrane is stretched laterally by a factor of about 2 to about 8 times. In another embodiment, the membrane is stretched longitudinally by a factor of about 2 to about 5 times. In yet another embodiment, the membrane is longitudinally stretched by a factor of about 2.5 to about 3.5, or about 3 times. In yet another embodiment, the membrane is stretched longitudinally by a multiple of about 3. In some embodiments, the membrane is stretched laterally by a factor of about 1.7 to about 8. In another embodiment, the membrane is longitudinally stretched by a factor of about 1.7 to about 5. In yet another embodiment, the membrane is longitudinally stretched by a factor of about 2.5 to about 3.5, or about 3 times.

In embodiments where uniaxial stretching is used, stretching may be carried out in the machine direction between a series of stretching rollers, nip rollers or vacuum rollers in the range of about 18-120°C. In some embodiments, the stretching may be performed at room temperature (approximately 18-22°C). The speed of the second draw roller is typically greater than the speed of the first nip roller, which facilitates stretching of the film. Stretching with a roller stretches the membrane in the machine direction, which can increase the length of the membrane and reduce the width or thickness of the membrane. In some embodiments, the membrane is stretched longitudinally by a factor of about 0.5 to about 80-50%. In addition, the tension of the web can be controlled so that further stretching on the order of 0-25% can be achieved.

The speed of the membrane through the longitudinal and transverse stretchers can be varied, and different speeds result in different amounts of stretching in the longitudinal and transverse directions. The stretching operation can be performed multiple times in each direction, for example, twice, three times or more in each direction. In one embodiment, the membrane is stretched first in the machine direction to the desired rate and then in the transverse direction to the desired rate.

After stretching, the film may be heat set and an annealing process performed to achieve greater dimensional stability. The annealing process can heat the web between 100°C and as high as 135°C. Depending on the speed of the process, the residence time to heat the membrane can be between about 0.5 minutes and as long as 5 minutes.

Polyethylene and UPE membranes are porous in the embodiments disclosed herein and have a post-stretch thickness in the range of about 6 microns and about 40 microns, or in the range of about 20 microns to about 40 microns. .. In a preferred embodiment, the UPE membrane has a post-stretch thickness within the range of about 25 microns and about 35 microns, or within the range of about 27 microns and about 30 microns. Thinner membranes have lower pressure drop across the membrane, which contributes to improved air permeability. The thickness of the stretched film depends largely on the starting thickness of the film and the stretch ratio. Thus, thinner stretched membranes can be made by starting with thinner membranes.

The inventors have found that stretching polyethylene porous membranes or UPE porous membranes in various embodiments can significantly increase air permeability without significantly increasing the pore size of the membrane. When the membrane is stretched, the apparent density of the polyethylene or UPE membrane is reduced according to formula (I). Stretched PE or UPE membranes, for example, have a higher porosity and therefore a lower apparent density compared to unstretched PE or UPE membranes.
Apparent density=weight/(area×thickness) (I)

The hydrophobicity of the vent membrane can be increased by surface modifying a gamma ray stable porous membrane such as a polyethylene porous membrane or a UPE membrane with a hydrophobic monomer. In some embodiments, the hydrophobicity of the polyethylene or UPE membrane can be increased by grafting a hydrophobic monomer onto the surface of the polyethylene or UPE membrane. Grafting refers to the chemical bonding of moieties such as monomers or other molecules to the surface of porous polymeric membranes, including the inner pore surface of the porous membrane. In other embodiments, other hydrophobic monomers can be utilized for coating rather than grafting a porous PE or UPE membrane. Hydrophobic monomers can be polymerized by free radical polymerization and cross-linked, eg, polyethylene, which is directly coated rather than grafted over the surface of the membrane with a cross-linked polymer formed from hydrophobic monomers and cross-linking agents. Membranes or UPE membranes can be provided. The monomer and the cross-linking agent can be polymerized by energy from an energy source such as an ultraviolet lamp, and the surface-modified porous membrane has substantially the same air permeability (within 10% or less) as the uncoated membrane. Have.

The grafted monomer is a fluorinated monomer, preferably a perfluorinated monomer, both of which reduce the surface energy of the membrane. A decrease in surface energy corresponds to an increase in membrane hydrophobicity. The perfluorinated compound is an organic fluorine compound containing only a carbon-fluorine bond or a carbon-carbon bond, and may contain another hetero atom. The fluorinated compound may contain some carbon-hydrogen bonds. Fluorinated and perfluorinated monomers have, for example, a straight or branched carbon backbone of carbon in the range of 1-20. Monomers with more carbon in the backbone and monomers with more fluorine substituents lead to grafted membranes with reduced surface energy.

In some embodiments, the grafted monomer is a perfluoroacrylate monomer. In some embodiments, the monomer is a perfluoro-n-alkyl acrylate monomer. The term "alkyl" as used herein has a specified number of carbon atoms and is substituted with at least one fluorine atom and is preferably perfluorinated, both monovalent saturated, both branched and straight chain. Refers to an aliphatic hydrocarbon group. Examples of suitable alkyls include, for example, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl, t-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, n-eicosadecyl, 2- Included are methylbutyl, 2-methylpentyl, 2-ethylbutyl, 3-methylpentyl, 4-methylpentyl. In a preferred embodiment, the monomer is perfluoro-n-octyl acrylate.

To graft the monomer onto the polyethylene membrane or onto the UPE membrane, the membrane is wet with an alcohol such as isopropyl alcohol (IPA). The alcohol dampening liquid can include a Type II photoinitiator such as benzophenone. The membrane is then immersed in a grafting solution (detailed in wt% in the examples below). In one embodiment, the grafting solution comprises perfluoro -n- octyl acrylate dissolved in decamethyl tetrasiloxane. The monomer is insoluble in water and a suitable solvent dissolves the monomer well without dissolving the benzophenone applied on the membrane. One such suitable solvents are decamethyl tetrasiloxane. Excess grafting solution can be removed from the porous membrane by squeezing the membrane using a roller (or a similar treatment). The impregnated membrane is then exposed to electromagnetic radiation or another suitable energy source to graft the moieties onto the porous polymeric membrane surface, including the inner surface of the pores. The electromagnetic radiation can be in the ultraviolet region of the spectrum or, in some cases, in the range of about 200 nm to about 600 nm. After exposure to electromagnetic radiation, the membrane can be washed, for example, in deionized (DI) water and then again in methanol. After washing, the membrane can be dried in an oven at about 50°C for about 5 to about 15 minutes.

Grafting a hydrophobic monomer onto a polyethylene film or UPE film reduces the surface energy of the film. The change in surface energy correlates with the amount of monomer grafted on the membrane. Increasing the concentration of monomer in the grafting solution increases the amount of monomer grafted on the PE or UPE membrane. The reduction and increase in the time of exposure of the membrane to electromagnetic radiation contribute to the reduction and increase in the degree of monomer grafting on the PE or UPE membrane, respectively. Increasing and decreasing the intensity of electromagnetic radiation can also increase and decrease the amount of grafting, respectively. Therefore, varying the monomer concentration in the grafting solution, the exposure time to electromagnetic radiation and the intensity of electromagnetic radiation can change the amount of monomer that is grafted, and thus the surface energy of the grafted membrane.

The porosimetry bubble point test method measures the pressure required to force air through the wet pores of a membrane. The bubble point test is a well known method for measuring or characterizing the pore size of membranes.

Bubble point can be measured by mounting a disc, such as a 47 mm disc of a dried membrane sample, in a holder. A small amount of IPA:water 60:40 mixture is placed upstream of the membrane to wet the membrane. The pressure is then gradually increased to force air through the pores of the membrane. The visual bubble point of the membrane is measured by the minimum pressure required to drive 60% IPA out of at least one pore of the wetted membrane.

Surface energy is also the same as surface tension, but represents the force per unit length, typically the force in dyne units required to break a film about 1 cm long (eg, dyne/cm). ) Is explained. For membranes, higher surface energy means that the membrane is more hydrophilic (or more non-hydrophobic) and lower surface energy means that the membrane is more non-hydrophilic (or more hydrophobic). Means All surface energy values reported herein are measured at room temperature unless otherwise noted. Grafted membranes typically have lower surface energy than non-grafted membranes.

The membrane of the present disclosure is housed in an appropriate device depending on the purpose of use. Examples of suitable devices for degassing are described in US Pat. Nos. 8,852,324 and 8,430,114. An example of a device suitable for degassing is described in US Pat. No. 5,053,060. An example of a device suitable for membrane distillation is described in US Patent Application Publication No. 2011/0132826 (A1). Each of the different applications has different pore size requirements, as will be appreciated by those skilled in the art.

Exemplary implementations include:
Embodiment 1. A grafted porous polyethylene membrane,
a) air permeability in the range of about 4.9 slpm/cm ^{2 to} about 9.4 slpm/cm ² when measured at 10 psi;
b) a surface energy in the range of about 15 dyne/cm to about 25 dyne/cm;
c) a liquid entry pressure in the range of about 5 psi to about 25 psi, as measured in a methanol:water 80:20 solution; and d) comprising perfluorinated monomer grafted to one or more surfaces of the membrane, Grafted porous polyethylene membrane.
Embodiment 2. The membrane of embodiment 1, wherein the perfluorinated monomer is a perfluoro-n-alkyl acrylate.
Embodiment 3. The membrane of embodiment 1, wherein the perfluorinated monomer is perfluoro-n-octyl acrylate.
Embodiment 4. The membrane of embodiment 1, wherein the air permeability is in the range of about 4.9 slpm/cm ^{2 to} about 6.1 slpm/cm ² as measured at 10 psi.
Embodiment 5. The membrane of embodiment 1, wherein the air permeability is about 5.4 slpm/cm ² , measured at 10 psi.
Embodiment 6. The membrane of embodiment 1, wherein the surface energy is in the range of about 21 dyne/cm to about 23 dyne/cm.
Embodiment 7. The membrane of embodiment 1, wherein the surface energy is about 21.5 dyne/cm.
Embodiment 8. The membrane of embodiment 1, wherein the liquid entry pressure is in the range of about 20 psi to about 25 psi as measured in a methanol:water 80:20 solution.
Embodiment 9. The membrane of embodiment 1, wherein the liquid entry pressure is about 22 psi, as measured in a methanol:water 80:20 solution.
Embodiment 10. The air permeability is about 5.4 slpm/cm ² , the surface energy is about 21.5 dyne/cm, and the liquid entry pressure is measured in methanol:water 80:20 solution when measured at 10 psi. The membrane of claim 1, wherein the membrane is about 22 psi when applied.
Embodiment 11. The membrane of embodiment 1, which is bacteria-retentive.
Embodiment 12. The membrane of embodiment 1, which is uniaxially or biaxially stretched.
Embodiment 13. The membrane of embodiment 1, which exhibits IR absorption corresponding to ester groups and corresponding to carbon-fluorine stretching.
Embodiment 14. 14. The membrane of claim 13 having an IR absorption corresponding to ester groups at about 1760 cm- ¹ .
Embodiment 15. The membrane of embodiment 13, wherein the IR absorption corresponding to the carbon-fluorine stretch is between about 1289 cm ^-1 and about 1114 cm ^-1 .
Embodiment 16. 14. The membrane of embodiment 13, wherein the area of the ester groups divided by the total peak area corresponding to polyethylene stretch is about 0.024.
Embodiment 17. A method for producing a surface-modified porous polyethylene membrane, comprising:
a) contacting the polyethylene membrane with an alcohol solution containing benzophenone;
b) contacting the polyethylene membrane with the grafting solution,
i) perfluorinated monomer; and ii) a membrane comprising a decamethyl tetrasiloxane process for surface modification; exposing and c) film to electromagnetic radiation, thereby comprising the step of causing the surface-modified porous ultrahigh molecular weight polyethylene membrane, Method.
Embodiment 18. The method according to embodiment 17, wherein the perfluorinated monomer is a perfluoro-n-alkyl acrylate.
Embodiment 19. The method according to embodiment 17, wherein the perfluorinated monomer is perfluoro-n-octyl acrylate.
Embodiment 20. The method of embodiment 17, wherein the surface modified porous ultra high molecular weight polyethylene membrane has an air permeability in the range of about 4.9 slpm/cm ^{2 to} about 9.4 slpm/cm ² when measured at 10 psi. ..
Embodiment 21. 18. The method of embodiment 17, wherein the surface modified porous ultra high molecular weight polyethylene membrane has a surface energy in the range of about 15 dyne/cm to about 25 dyne/cm.
Embodiment 22. 18. The method of embodiment 17, wherein the surface modified porous ultra high molecular weight polyethylene membrane has a liquid entry pressure in the range of about 5 psi to about 25 psi when measured in a methanol:water 80:20 solution.
When measured in embodiments 23.10Psi, about 5.9slpm / cm ² - a polyethylene film having a bubble point in the range of about 9.4slpm / cm ² air permeability in the range of and about 12psi- about 19psi And a polyethylene membrane having a molecular weight in the range of about 2,000,000 daltons to about 9,000,000 daltons.
Embodiment 24. A method of venting, comprising the step of flowing a gas through the surface-modified polyethylene membrane according to any of the preceding claims.
Embodiment 25. A method of degassing comprising the step of diffusing steam through a surface modified polyethylene membrane according to any of the preceding claims.
Embodiment 26. A method of membrane distillation comprising passing steam through a surface modified polyethylene membrane according to any of the preceding claims.
Embodiment 27. A vent membrane comprising an expanded porous polyethylene membrane and a perfluorinated monomer that modifies one or more surfaces of the expanded porous polyethylene membrane, which is bacteria-retentive as determined by ASTM F838-05, and:
e) when measured at 10 psi, about 4.9slpm / cm ² - an air permeability in the range of about 9.4slpm / cm ^2; and f) from about 15 dyne / cm- surface energy in the range of about 25 dyne / cm A vent membrane.
Embodiment 28. A vent membrane according to embodiment 27, having a tensile stress measured in the longitudinal direction of about 8 MPa to about 12 MPa in megapascals and about 0.2 mm/mm to about 0.3 mm/mm in millimeters/millimeters. After gamma-irradiating the vent membrane with tensile strain and with a gamma-ray dose of at least about 25 kGy, the tensile stress measured in the crossweb direction is from about 5 MPa to about 8 MPa in megapascals and about 0. 3 mm/mm-vent membrane having a tensile strain of about 0.5 mm/mm.
Embodiment 29. 29. The vent membrane according to any one of embodiments 27-28, wherein the stretched porous polyethylene membrane is biaxially stretched.
Embodiment 30. The vent membrane according to any one of embodiments 27-29, wherein the expanded porous polyethylene membrane is ultra high molecular weight polyethylene.
Embodiment 31. A vent membrane according to any one of embodiments 27 to 30, wherein the perfluorinated monomer comprises perfluoro-n-alkyl acrylate.
Embodiment 32. Any one of embodiments 27-31, wherein the vent membrane comprising a perfluorinated monomer that modifies one or more surfaces of the expanded porous polyethylene membrane has a surface energy in the range of 21 dyne/cm-23 dyne/cm. Bent membrane described in 1.
Embodiment 33. The stretched porous polyethylene membrane before gamma ray treatment has a tensile stress measured in the longitudinal direction of about 12 MPa to about 16 MPa in megapascals and about 0.5 mm/mm to about 0.9 mm/mm in millimeters/millimeters. The stretched polyethylene film has a tensile strain and has a tensile stress of about 6 MPa to about 8.5 MPa in megapascals measured in the cross-web direction and about 1.0 mm/mm to about 1. 33. The vent membrane according to any one of embodiments 27-32, having a tensile strain of 8 mm/mm.
Embodiment 34. A vent filter comprising the vent membrane according to any one of embodiments 27 to 33, wherein the vent membrane is fixed to the housing.
Embodiment 35. A method for manufacturing a vent membrane, comprising:
a) Wetting the porous polyethylene membrane with a solution containing benzophenone, wherein the stretched porous polyethylene membrane has a tensile stress of about 12 MPa to about 16 MPa in megapascals measured in the machine direction and about a millimeter/millimeter. The tensile polyethylene membrane has a tensile strain of 0.5 mm/mm-about 0.9 mm/mm, and the stretched polyethylene membrane has a tensile stress of about 6 MPa-about 8.5 MPa in millimeters/millpascals measured in the crossweb direction and a millimeter/ Having a tensile strain in millimeters of about 1.0 mm/mm to about 1.8 mm/mm;
b) a stretched polyethylene membrane,
i) perfluorinated monomer; and ii) contacting the grafting solution containing decamethyl tetrasiloxane; and c) membrane was exposed to electromagnetic radiation, and comprising the step of grafting the monomers to the porous polyethylene membrane, method.
Embodiment 36. The vent membrane according to embodiment 35, wherein the porous polyethylene membrane is biaxially stretched.
Embodiment 37. The vent membrane according to any one of embodiments 35 to 36, wherein the porous polyethylene membrane is ultra-high molecular weight polyethylene.
Embodiment 38. 38. The vent membrane according to any one of embodiments 35-37, wherein the perfluorinated monomer comprises perfluoro-n-alkyl acrylate.
Embodiment 39. A vent membrane produced by the method of any one of embodiments 35-38, which is bacteria-retentive as determined by ASTM F838-05, and:
g) when measured at 10 psi, about 4.9slpm / cm ² - an air permeability in the range of about 9.4slpm / cm ^2; and h) from about 15 dyne / cm- surface energy in the range of about 25 dyne / cm A vent membrane.
Embodiment 40. A vent membrane according to embodiment 39, having a tensile stress measured in the longitudinal direction of about 8 MPa to about 12 MPa in megapascals and about 0.2 mm/mm to about 0.3 mm/mm in millimeters/millimeters. After gamma-irradiating the vent membrane with tensile strain and with a gamma-ray dose of at least about 25 kGy, the tensile stress measured in the crossweb direction is from about 5 MPa to about 8 MPa in megapascals and about 0. 3 mm/mm-vent membrane having a tensile strain of about 0.5 mm/mm.
Embodiment 41. A vent membrane comprising a gamma-stable porous polymer membrane and a perfluorinated monomer that modifies one or more surfaces of the porous polymer membrane, which is bacteria-retentive as determined by ASTM F838-05, and:
i) air permeability in the range of about 4.9 slpm/cm ^{2 to} about 9.4 slpm/cm ² when measured at 10 psi;
j) a surface energy in the range of about 15 dyne/cm to about 25 dyne/cm; and a tensile strain of about 0.2 mm/mm to about 0.3 mm/mm in millimeters/millimeters measured in the machine direction, And after gamma-irradiation of the vent membrane with a gamma-ray dose of at least about 25 kGy, a tensile stress of about 5 MPa-about 8 MPa in megapascals measured in the cross-web direction and about 0.3 mm/mm-about mm/mm. A vent membrane having a tensile strain of 0.5 mm/mm.

General Experiments: Membrane Stretch UPE membranes are preheated at 100°C. The preheated membrane is then stretched longitudinally (longitudinal) in two nips (closed rollers). The speed of each successive nip is greater than the speed of the previous nip. Therefore, if the speed of each nip increases 1.4 times, the speed of the second nip increases 1.4×1.4=1.96 times. The membrane is then cooled through about two more rollers to about 60°C-70°C. As the membrane exits the longitudinal stretch section, the length of the membrane is approximately doubled and the width of the membrane is reduced from about 12 inches (30.5 cm) to about 9.5 inches (24.1 cm).

The longitudinally stretched membrane is then fed to a cross-web stretcher (also called a tenter). The membrane is fed into the tenter by a longitudinally advancing clip. The clip travels in a 10 foot (3.0 meter) preheated oven, which then travels in a V-shape in the extension zone oven, thus stretching the membrane laterally. The temperature of the preheated oven is about 100°C and the temperature of the extension zone is about 105°C. The membrane then proceeds in an annealing zone where the clips remain parallel. The annealing zone temperature is set 5-15 degrees Celsius above the extension zone, but at least 5 degrees Celsius below the melting point of the polymer. Stretching operations are performed at about 3 feet (0.9 meters)-10 feet (3.0 meters) per minute, depending on the stretch ratio.

General Experiment: Visual Bubble Point The visual bubble point test method measures the pressure required to force air through a wet pore in a membrane.

The test was carried out by mounting a 47 mm disc of the dried membrane sample in a holder. The holder is designed to allow an operator to put a small amount of IPA:water 60:40 mixture upstream of the membrane to wet the membrane. The pressure is then gradually increased to force air through the pores of the membrane. The visual bubble point of the membrane is measured by the minimum pressure required to drive 60% IPA out of at least one pore of the wetted membrane.

General Experiment: Air Permeability Dry 47 mm membrane discs were placed in a holder and the air permeability at 10 psi (69 kPa) was recorded using a flow meter at standard liters/minute (slpm) to determine the permeability. The air permeability was measured by calculating the value of slpm/cm ² .

Example 1
Example 1 shows the effect of stretching a UPE membrane with a nominal 0.1 micron pore size (92 micron thickness). The visual bubble point and air permeability of the membrane were measured. For comparison, visual bubble point and air permeability of 0.2 micron polytetrafluoroethylene (PTFE) membrane (40 micron thick) and 0.2 micron polyvinylidene fluoride (PVDF) (115 micron thick) membrane. I also confirmed.

A 92 micron thick film sample was stretched twice in the machine and cross-web directions to a thickness of 30 microns. The visual bubble point and air permeability of the membrane were measured as described in the general experimental part. The results of this experiment are shown in Table 1, which shows that the membrane's visual bubble point drops from 32 psi to 19 psi on extension while air permeability from 0.49 (slpm/cm ² ) at 10 psi. It shows a 12-fold increase in 5.9 standard liters/minute/area (slpm/cm ² ) (see Table 1, UPE 0.1 micron and UPE 0.1 micron (extension 2×2)). Stretched UPE membranes have superior air permeability compared to nominal 0.2 micron PTFE and PVDF membranes.

Example 2
Example 2 shows the effect of stretching a UPE membrane with a nominal 0.2 micron pore size on the membrane's visual bubble point and air permeability.

A 90 micron membrane sample was stretched 3 times in the machine direction and 4 times in the crossweb direction to give a thickness of 27 microns. The visual bubble point and air permeability of the membrane were measured as described in the general experimental part. The results of this experiment show that the visual bubble point of the membrane dropped from 19 psi to 12 psi upon stretching while the air permeability at 10 psi increased from 1.97 to 9.4 slpm/cm ² .

Example 3
Example 3 describes the preparation of a benzophenone solution.

0.16 grams of benzophenone (99%, Sigma-Aldrich) was dissolved in 40 ml of isopropyl alcohol (IPA) to give a 0.4 wt% benzophenone solution.

Example 4
Example 4 describes the preparation of a grafting solution containing a perfluorinated monomer.

4g perfluoro -n- octyl acrylate (97% Exfluor Research Corporation) and a solution containing a decamethyl tetrasiloxane (97% sigma) of 36g was prepared.

Example 5
Example 5 describes the surface modification of stretched UPE membranes.

A 47 mm disc of the stretched UPE membrane of Example 1 was wetted with the 0.4% benzophenone solution described in Example 3 for 25 seconds. The membrane disc was then dried at room temperature for 5 minutes. The dried membrane disc was then placed in the grafting solution described in Example 4. The dish was covered and the membrane was immersed in the grafting solution for 2 minutes. The membrane disc was removed and sandwiched between 1 mil polyethylene sheets. Excess solution was removed by rolling a rubber roller on it so that the polyethylene/membrane disc/polyethylene sandwich was flat on the table. The polyethylene sandwich was then taped to a delivery unit that delivered this assembly into a Fusion Systems Broadband UV exposure lab unit emitting at a wavelength of 200 nm to 600 nm. The exposure time is controlled by the speed at which this laminate moves through the UV unit. In this example, the laminate traveled at 7 feet/minute (2.1 meters/minute) in the UV chamber. After coming out of the UV unit, the membrane was taken out of the sandwich and immediately put into methanol and stirred in it for 5 minutes for washing. After this washing procedure, the membrane was dried for 10 minutes on the holder in an oven operating at 50°C.

The resulting membrane had an air permeability of 5.44 slpm/cm ² at 10 psi, with the air permeability of the grafted porous membrane being substantially the same, or ± of the air permeability of the starting porous membrane. It was shown to be within 10%.

Example 6
Example 6 shows the surface energy of the modified stretched UPE membrane of Example 5.

The surface energy of the surface-modified stretched UPE membrane described in Example 5 was measured by adding a small amount of IPA:water solution to the membrane surface and examining the volume percent of IPA in water to wet the membrane. The wetting liquid makes the surface of the membrane translucent immediately after a small amount of the solution touches the membrane. The surface energy of the wetting liquid is considered the surface energy of the membrane.

The results of this experiment are shown in Table 2. Only 100% IPA with a surface energy of 21.22 dyne/cm wets the surface modified stretch film. By comparison, a nominal 0.2 micron unmodified PTFE membrane has a surface energy of 21.75 dyne/cm [Der Chemica Sinica, 2011, 2(6):212-221]. These results indicate that the surface modified expanded UPE membrane is more hydrophobic than the PTFE membrane.

Example 7
Example 7 shows the liquid entry pressure of the modified stretched UPE membrane of Example 5.

A 47 mm disc of modified stretched membrane from Example 5 was placed in a filter holder connected to a reservoir containing 100 ml of methanol:water 80:20 mixture. A pressure regulator connected to the reservoir was used to gradually increase the pressure until liquid passed from upstream to downstream of the membrane in the filter holder. The minimum pressure required to force a liquid through the pores of a dried membrane is defined as the membrane's liquid entry pressure.

The results of this experiment indicated that the liquid modified extension membrane had a liquid entry pressure of 17 psi. By comparison, the 0.2 micron PTFE membrane had a liquid entry pressure of 6 psi. The results show that the surface-modified stretched UPE protects against wetting more than PTFE and, therefore, protects against wetting than PTFE when used in an application environment.

Example 8
Example 8 shows liquid bacterial retention of stretched UPE membranes.

References: This study was conducted based on the following references: ASTM International F838-05/R (2013) Standard Test Method for Determining Bacterial Retention of Membrane Filters Utilized for Liquid Filtration. ISO 10993-12, 2012, Biological Evaluation of Medical Devices-Part 12:Sample Preparation and Reference Materials, which specifies requirements for sample preparation.; And ISO/IEC 17025, 2005, General Requirements for the Competence of Testing and Calibration Laboratories, which specify requirements for calibration and testing.

General procedure: Three test article filters (SUPGP047000, prepared according to Example 2) with three positive control filters (HVHP047000, 0.45 micron PVDF membrane expected not to retain 100% bacteria). Preassembled in the filter housing unit. Prior to testing, all units were sterilized by gravity displacement steam sterilization (121° C., 15 minutes), annealed to ambient temperature, and the assembly torqued to seal the filter assembly. Test article filters and control filters were pre-wetted with 70% filter sterilized isopropanol (IPA) followed by sterile deionized water (DI water). Appropriate accessories (piping and collection vessels) were prepared (assembled and sterilized) for integration with the building vacuum and for testing bacterial retention. A bacterial challenge of Pseudomonas diminuta (ATCC #19146) was prepared by streaking aliquots from frozen stock on TSA agar plates. After the streak incubation, the microorganisms were harvested in an inoculation loop in 10-20 mL of nutrient broth. The suspension was then adjusted using a spectrophotometer to a density above 1×10 ⁷ CFU/mL, inoculation verification after serial dilution, plating on TSA, and 30-35° C. for about 4 days. Confirmed by incubation. Samples were seeded with 3 mL of bacterial challenge through the upper inlet port of the filter assembly. Bacterial challenge was withdrawn from the filter samples under a building vacuum of approximately 6 psi. The filtrate is then recovered and B. The presence or absence of diminuta (complete recovery) was evaluated. The recovery filters were then transferred to Trypticase Soy Agar (TSA) plates and incubated at 30-35°C for 7 days. Positive controls were challenged in the same way and the collected filtrates were evaluated for bacterial retention after serial dilution and smear plating in duplicate. A single negative control was included in this study where sterile nutrient broth served as the challenge medium. Testing of phosphate buffered saline (PBS), nutrient broth and deionized water (used for pre-wetting) showed that the medium used for this study was sterile (data not shown).

The results of Example 8 show that the stretched UPE membrane prepared according to Example 2 has a B.I. It shows that the bacteria retains 100% of diminuta bacteria and is bacteria retaining as judged by passing ASTM F838-05/R (2013).

Example 9: Scanning electron microscopy (SEM)
Scanning electron microscopy can be used to observe the surface of the membrane to determine if changes have occurred to the membrane surface during the stretching process.

Samples of nominal 0.1 micron film (32 psi visual BP in 60% IPA) before and after stretching according to Example 1 were gold sputtered and then from the FEI Quanta 200 SEM System (FEI Company, Hillsboro, Oreg.). Available) and scanned at an accelerating voltage of 10 kV. 1A-B are SEM images of symmetrical unstretched UPE membrane and symmetrical stretched UPE membrane, respectively. A 5000× magnification was used in each case.

The stretching process leads to a more open structure, which achieved high air permeability due to the side-by-side fibrils extending between the nodes that hold the particles.

Example 10
This example illustrates the effect of the disclosed stretching process on the mechanical properties of the membrane.

The tensile strain at break of the membrane before and after stretching (according to Example 1) was measured using an Instron(TM) Force Transducer model 2519-102, an Instron(TM) model 3342 Compression/Tensile instrument equipped with a computer and Blue Hill software. evaluated.

Testing was performed by continuous pulling one sample from each film in the machine direction and the cross-web direction until breaking. The sample was cut into 1" x 4.5" dimensions using a metal die cutter.

2A-B show the stress-strain curves in the machine direction (MD) (FIG. 2A) and cross-web (CW) direction (FIG. 2B) for unstretched UHMWPE membrane (blue) and stretched UHMWPE membrane (red). After stretching, the tensile fracture strain of the film is reduced to about 1/8 in MD and 5.5 in CW.

2A-B show that a non-expanded porous polyethylene membrane has a tensile stress measured in the machine direction of about 10 MPa to about 14 MPa in megapascals and about 4.5 mm/mm to about 5.5 mm/mm. An unstretched film having a tensile strain of mm and a tensile stress of about 6.5 MPa in megapascals-about 8.5 MPa and a value of about 7.0 mm/mm-in millimeters/millimeters-measured in the cross-web direction. It has a tensile strain of about 9.5 mm/mm. The graph further illustrates that the expanded porous polyethylene membrane has a tensile stress measured in the longitudinal direction of about 12 MPa to about 16 MPa in megapascals and a tensile stress of about 0.5 mm/mm to about 0.9 mm/mm in millimeters/millimeters. The strained and vent membrane has a tensile stress of about 6 MPa to about 8.5 MPa in megapascals measured in the crossweb direction and about 1.0 mm/mm to about 1.8 mm/mm in millimeters/millimeters. It has a tensile strain of.

Example 11
This example demonstrates the effect of gamma sterilization on the mechanical properties of stretched membranes.

Membranes stretched according to Example 1 and modified according to Example 5 were used in this example. A 15 x 30 cm membrane sheet was placed in a sealed polyethylene bag and exposed to a gamma ray dose of 30.6 kGy for 395 minutes.

The tensile strain at break of the membranes before and after gamma irradiation was evaluated using an Instron™ Model 3342 Compression/Tensile instrument equipped with an Instron™ Force Transducer model 2519-102, computer and Blue Hill software.

Each film was tested by continuous pulling two samples in the machine direction and two samples in the crossweb direction until breaking. The sample was cut into 1" x 4.5" dimensions using a metal die cutter.

FIGS. 3A-B show longitudinal (MD) orientation (FIG. 3A) and cross-web in stretched UHMWPE membrane (green dotted line), gamma-ray exposed stretched UHMWPE membrane (red) and gamma-exposed stretched and surface modified UHMWPE membrane (blue). The stress-strain curve of a (CW) direction (FIG. 3B) is shown. The tensile fracture strain of the stretched film and the surface modified-stretched film was reduced by approximately 2.5 times in MD and 3.3 times in CW after the gamma ray exposure and before the gamma ray exposure. The tensile fracture strains of modified and unmodified stretched membranes are similar after gamma-ray exposure, indicating a minimal effect of surface modification on the mechanical properties of stretched membranes.

3A-B show that after gamma-ray treatment of the vent membrane with a gamma-ray dose of at least about 25 kGy, the vent membrane still has a tensile stress measured in the longitudinal direction of about 8 MPa to about 12 MPa in millimeters per millimeter and a tensile stress of about 12 MPa. 0.2 mm/mm to about 0.3 mm/mm tensile strain, and the vent membrane has a tensile stress of about 5 MPa to about 8 MPa in millimeters per millimeter measured in the cross-web direction and millimeters/millimeter. It has a tensile strain of about 0.3 mm/mm to about 0.5 mm/mm.

Example 12
This example describes ATR-FTIR spectroscopy of a surface modified stretch film.

The amount of monomer grafted to the membrane surface was determined by ATR-FTIR ("ATR") spectroscopy in the form of peak ratios. ATR measurements were performed using a Bruker Tensor 27 FTIR equipped with an ATR assembly containing germanium crystals. All spectra were recorded with 32 scans and a resolution of 4 cm-1. The background was bare crystals. FIG. 4 is an IR spectrum of the stretched film of Example 5 before (dotted line) and after grafting (solid line). The spectra after grafting were offset by 0.6 absorbance units for ease of viewing. After surface modification, graft film is, 1760 cm ^-1 (corresponding to the acrylates peak) and in the range of 1289-1114cm ^-1 - shows characteristic peaks at (carbon corresponding to fluorine stretch). The resulting peak area of 1760 cm ^-1 using OPUS data collection program (corresponding to the UHMWPE stretch) 2918 and divided by the total peak area of 2850 cm ^-1, UHMWPE (ultra high molecular weight polyethylene) of monomer grafted on the surface An amount (0.024) was obtained.

Example 13
Example 13 describes the preparation of a benzophenone solution.

0.20 grams of benzophenone (99%, Sigma-Aldrich) was dissolved in 40 ml of isopropyl alcohol (IPA) to give a 0.5 wt% benzophenone solution.

Example 14
Example 14 describes the preparation of a grafting solution containing a perfluorinated monomer.

A solution containing 4 g 2-(perfluorobutyl)ethyl acrylate (97% Fluoryx) and 36 g Galden HT 135 (Solvay) was prepared.

Example 15
Example 15 describes surface modification of stretched UPE membranes.

A 47 mm disc of stretched UPE membrane was wetted with the 0.5% benzophenone solution described in Example 13 for 25 seconds. The membrane disc was then dried at room temperature for 5 minutes. The dried membrane disc was then placed in the grafting solution described in Example 14. The dish was covered and the membrane was immersed in the grafting solution for 2 minutes. The membrane disc was removed and sandwiched between 1 mil polyethylene sheets. Excess solution was removed by rolling a rubber roller on it so that the polyethylene/membrane disc/polyethylene sandwich was flat on the table. The polyethylene sandwich was then taped to a delivery unit that delivered this assembly into a Fusion Systems Broadband UV exposure lab unit emitting at a wavelength of 200 nm to 600 nm. The exposure time is controlled by the speed at which this laminate moves through the UV unit. In this example, the laminate traveled at 10 feet/minute in the UV chamber. After coming out of the UV unit, the membrane was removed from the sandwich and immediately put in isopropyl alcohol and stirred in it for 5 minutes to wash. After this washing procedure, the membrane was dried for 5 minutes on the holder in an oven operating at 65°C.

Example 16
Example 16 shows the surface energy of the modified stretched UPE membrane of Example 15.

The surface energy of the surface modified stretched UPE membrane described in Example 15 was measured by adding a small amount of IPA:water solution to the membrane surface and examining the volume percent of IPA in water to wet the membrane. The wetting liquid makes the surface of the membrane translucent immediately after a small amount of the solution touches the membrane. The surface energy of the wetting liquid is considered the surface energy of the membrane. The modified film in this case is wet in 60% IPA.

Example 17
Example 17 shows the liquid entry pressure of the modified stretched UPE membrane of Example 15.

A 47 mm disc of modified stretched membrane from Example 15 was placed in a filter holder connected to a reservoir containing 100 ml of methanol:water 80:20 mixture. A pressure regulator connected to the reservoir was used to gradually increase the pressure until liquid passed from upstream to downstream of the membrane in the filter holder. The minimum pressure required to force a liquid through the pores of a dried membrane is defined as the membrane's liquid entry pressure.

The results of this experiment showed that the liquid modified extension membrane had a liquid entry pressure of 7 psi.

INCORPORATION BY RESOURCES AND EQUIVALENTS The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety.

While the invention has been illustrated and described with respect to one or more embodiments, those skilled in the art will appreciate equivalent alterations and modifications upon reading and understanding the specification and the annexed drawings. The present invention includes all such modifications and alterations and is limited only by the scope of the following claims. Moreover, although certain particular features or aspects of the present invention may be disclosed with respect to only one of the several embodiments, such features or aspects may be desired for a given or particular application. , May be combined with one or more other features or aspects of other embodiments that may be advantageous. Further, the terms "includes," "having," "has," "with," or variations thereof, are used to implement the invention and the claims. In the use of any of the ranges, such terms are intended to include all as well as the term "comprising." Also, the term "exemplary" is intended only to mean an example rather than the best example. Also, the features and/or elements presented herein are shown with particular dimensions and/or orientations relative to each other for simplicity and ease of understanding, and actual dimensions and/or orientations may be It should be understood that it may differ significantly from that shown herein.

Although the present invention has been described in considerable detail with reference to that particular version, other versions are possible. For example, a vent membrane can be used for degassing to remove gas from a liquid. In addition, vent membranes can be used for membrane distillation. Still other stretch and surface modified membranes can be used as an integral or replaceable vent for single use liquid packaging. Still other stretch and surface modified membranes can be used in articles such as protective apparel and enclosures. Therefore, the spirit and scope of the appended claims should not be limited to the description and versions contained herein.

Claims (8)

A grafted porous ultra high molecular weight polyethylene membrane,
a) when measured at ^{10psi, 4.9 slpm / cm 2 -} 9.4 Air permeability in the range of slpm / cm ^2;
b) a surface energy in the range of 15 dyne/cm- 25 dyne/cm;
c) a liquid entry pressure in the range of 5 psi- 25 psi when measured in a solution of methanol:water in a ratio of 80:20 in aqueous methanol; and d) on one or more surfaces of the membrane. Grafted porous ultra-high molecular weight polyethylene membrane containing grafted perfluorinated monomer. The membrane of claim 1, wherein the perfluorinated monomer comprises perfluoro-n-alkyl acrylate or perfluoro-n-octyl acrylate. The membrane of claim 1, wherein the membrane is bacteria-retentive as determined by ASTM F838-05 . A vent membrane,
Comprise a sterile porous ultrahigh molecular weight polyethylene membrane, seen contains the perfluorinated monomers porous ultrahigh molecular weight polyethylene film is grafted to one or more surfaces of the porous ultrahigh molecular weight polyethylene membrane, ASTM F838-05 Bacterial retention as determined by:
a) when measured at ^{10psi, 4.9 slpm / cm 2 -} 9.4 Air permeability in the range of slpm / cm ^2;
b) a surface energy in the range of 15 dyne / cm- 25 dyne / cm ;及beauty,
have a tensile strain of 0.2 mm / mm- 0.3 mm / mm in tensile stress and millimeter / millimeters 8 MPa-12 MPa in megapascals measured in c) longitudinally, it is measured in the transverse direction A vent membrane having a tensile stress of 5 MPa- 8 MPa in megapascals and a tensile strain of 0.3 mm/mm- 0.5 mm/mm in millimeters/millimeters. A method for producing a surface-modified porous ultra high molecular weight polyethylene film, comprising:
a) contacting the ultra high molecular weight polyethylene membrane with an alcohol solution containing benzophenone;
b) contacting the ultra high molecular weight polyethylene membrane with a grafting solution,
a step of surface modification of a film containing and ii) decamethyl cyclotetrasiloxane;; i) perfluorinated monomers and c) film viewing including the step of exposure to electromagnetic radiation,
Surface modified porous ultra high molecular weight polyethylene membrane
a) when measured at 10 ^psi, the air permeability in the range of ^{4.9slpm / cm 2 -9.4slpm / cm 2} ;
b) a surface energy within the range of 15 dyne/cm-25 dyne/cm;
c) a liquid entry pressure within a range of 5 psi to 25 psi when measured in a solution of methanol:water in a ratio of 80:20 in an aqueous methanol solution; and
d) Perfluorinated monomers grafted on one or more surfaces of the membrane
Including the method. The step of contacting the ultra high molecular weight polyethylene membrane with the grafting solution comprises a longitudinally measured tensile stress of 12 MPa- 16 MPa in megapascals and 0.5 mm/mm- 0.9 mm in millimeters/millimeters. 6. The method of claim 5 , comprising stretching an ultra high molecular weight polyethylene membrane having a tensile strain of /mm; and contacting the extended ultra high molecular weight polyethylene membrane with a grafting solution. 7. The method of claim 6, wherein the ultra high molecular weight polyethylene membrane is uniaxially or biaxially stretched. The stretched ultra high molecular weight polyethylene membrane has a tensile stress of 6 MPa- 8.5 MPa measured in the transverse direction and a tensile strain of 1.0 mm/mm- 1.8 mm/mm in millimeter/mm. The method according to claim 6 or 7 , further comprising: